(1) Technical Field
This invention relates to a thermoplastic rubber composition. More particularly, this invention relates to a thermoplastic rubber composition with superior appearance, flexibility (feeling), mechanical strength and wear resistance.
(2) Description of the Related Art
A thermoplastic elastomer composition obtained by the so-called to speak dynamic crosslinking, that is crosslinking during melt mixing of a rubbery polymer such as a radically crosslinkable olefinic elastomer and a radically non-crosslinkable olefinic resin such as polypropylene (PP) in an extruder in the presence of a radical initiator, is already known technology and widely used in applications such as automotive parts.
As such an olefinic elastomer, ethylene-propylene-diene (EPDM) or an olefinic elastomer manufactured with a metallocene catalyst is known (JP-A-8-120127 and JP-A-9-137001). As the thermoplastic crosslinkable rubbers composed of an olefinic elastomer and a special polyolefin resin, a thermoplastic crosslinkable rubber composition consisting of an olefinic rubber, a decomposition type polyolefin and a crosslinking type polyolefin consisting of ethylene unit and xcex1-olefin unit having 4-10 carbon atoms (JP-A-60-231747) and a thermoplastic crosslinkable rubber composition composed of an olefinic rubber, a decomposition type polypropylene, a crosslinking type polyethylene and the like (JP-A-1-295818) are also disclosed. However, any composition in the above publications is not sufficient in appearance, flexibility (feeling) and mechanical strength, and thus there remains a need to a high strength thermoplastic rubber composition durable to practical uses.
Considering these problems, the object of the present invention is to provide a thermoplastic rubber composition which does not have the above described problems and is superior in appearance, flexibility (feeling), mechanical strength and wear resistance and also enables stabilized quality due to an improved productivity.
The present inventors found out unexpectedly, after thorough study to get a thermoplastic rubber composition with superior mechanical strength, that combined use of a rubbery polymer and a thermoplastic resin with specified characteristics dramatically enhanced mechanical strength and wear resistance while maintaining appearance and flexibility, and thus completed the present invention.
The present invention provides a thermoplastic rubber composition prepared by crosslinking 1-99 parts by weight of a crosslinkable rubbery polymer (A) and 1-99 parts by weight of a polypropylene resin (B) (total amount of (A) and (B) being 100 parts by weight), wherein said (B) comprises a polypropylene resin (B-1) characterized by generation of a torque higher than Mo after melting, and a polypropylene resin (B-2) characterized by generation of a torque not higher than Mo after melting, in a melting test of said (B) in the presence of an organic peroxide (temperature condition being at 200xc2x0 C.), wherein Mo is a torque right after complete melting.
The present invention also provides a thermoplastic rubber composition prepared by crosslinking 1-99 parts by weight of an ethylene/xcex1-olefin copolymer rubber of ethylene and an xcex1-olefin with 3-20 carbon atoms (Axe2x80x2) manufactured with a metallocene catalyst, and 1-99 parts by weight of a polyolefin resin (Bxe2x80x2) (total amount of (Axe2x80x2) and (Bxe2x80x2) being 100 parts by weight), wherein said (Bxe2x80x2) includes a polyolefin resin (B-1xe2x80x2) characterized by generation of a torque higher than Mo after melting (preferably a polyethylene resin and/or a polyolefin resin comprising xcex1-olefin units with 4-20 carbon atoms), and a polyolefin resin (B-2xe2x80x2) (preferably a polypropylene based block copolymer resin or a polypropylene homopolymer resin) characterized by generation of a torque not higher than Mo after melting, in a melting test of said (Bxe2x80x2) in the presence of an organic peroxide (temperature condition being at 200xc2x0 C.), wherein Mo is a torque right after complete melting.
A thermoplastic rubber composition of the present invention is superior in appearance, flexibility (feeling) and mechanical strength and enables stabilized quality due to an improved productivity.
A composition of the present invention can be used in wide applications including automotive parts, automotive interior parts, air bag covers, machine parts, electrical parts, cables, hoses, belts, toys, miscellaneous goods, daily necessaries, construction materials, sheets and films, and thus has a big industrial role.